Another thing that games sometimes have rules for is exposure to various types of weather and temperature extremes. Often these rules never get used, since most of the time GMs just sort of tend to assume the weather is nondescript. That's fine most of the time (unless you are running a Viking colonists campaign in Greenland).

And it's often just easier to assume the weather is never bad enough to cause serious problems. Because weather is an insidious hazard - you can't beat it off like an attacking monster. It constantly gnaws away at your endurance and you just need to find shelter. And if you don't manage that, you're basically dead. So it's tricky to incorporate into a game and maintain a sense of drama without simply being too deadly. It works okay in fiction (see the attempted crossing of the Mountains of Moria in The Lord of the Rings) because the writer can always get the heroes to shelter in time. In a game, you need to be a lot more careful.